the chemistry of everything kimberley waldron...ether and alcohol: isomers • diethyl ether was the...

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©2007 Pearson Prentice Hall 1

Chapter 9: ExplosivesA Study of Organic Molecules with Simple

Functional Groups and the Forces within

Them

The Chemistry of Everything

Kimberley Waldron

Richard Jarman,

College of DuPage


Chapter 9 Topics

• Combustion reactions and explosions.

• Endothermic and exothermic reactions.

• Alkanes, alkenes, and alkynes.

• Hydrocarbon nomenclature.

• Cis–trans isomerism.

• Ethers.

• Bond energies.

• High explosives and low explosives.

• Entropy and the second law of thermodynamics.

• Gas chromatography.

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Gunpowder Plot

• Guy Fawkes is a

celebration of organic

chemistry.

• The nucleus provides

huge energy through

nuclear reactions.

• Traditional explosives

have used chemical

reactions.


Gunpowder

• Gunpowder uses oxidation of carbon.

• The reactants have elements C and S.

• Products contain C and S bound with O.

• The reactants are solids.

• Many of the products are gases.

• Conversion of solid to gas creates blast.

3222324210()11()4()5()5()5()()3()KNOsCsSsCOgCOgNgKCOsKSOsKS+ + + + + + +

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Heat and Expansion

• The gunpowder explosion

is a combustion reaction.

• Reaction between fuel

(sulfur and carbon) and

oxygen produces heat.

• Heat is not sufficient to

produce an explosion.

• The reaction must occur

in confined space.


The Gunpowder Car?

• The use of explosive energy to power a

vehicle was recognized, but not

successfully realized with gunpowder.

• Internal combustion engines use

explosions to create motion, but use

gasoline instead.

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Gasoline and Carbon: Things

in Common

• Gunpowder and gasoline are fuels.

• Both contain carbon:– Gunpowder contains the element carbon.

– Gasoline is a hydrocarbon that contains C and Hatoms.


Combustion of

Hydrocarbons• Hydrocarbons combine with oxygen to produce

carbon dioxide and water.

• All the products are gases:

– Carbon dioxide (CO2)

– Water (H2O)

• No solid residues.

• Maximize pressure to perform mechanical work.

8182222()25()16()18()CHlOgCOgHOg+ +

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Theory and Reality

• Combustion equations are expressions of

ideal combustion where only CO2 and H2O

are products.

• In limited oxygen incomplete combustionoccurs:

– Carbon monoxide is also produced.

– (21 O2 compared with 25 O2 with complete

combustion).

8182222()21()8()8()18()CHlOgCOgCOgHOg+ + +


Emissions and the

Environment

• Typical car engine results in about 5 %

CO.

• CO2 and CO are both greenhouse gases.

• CO is also a health hazard.

• Catalytic converters convert CO into CO2.

22()()()OgCOgCOg+

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What Makes a Good Fuel?

• In the combustion process:

– C-C and C-H bonds are broken.

– C-O and H-O bonds are made.

• The bonds that are made are stronger than those that

are broken – energy is released – exothermic reaction.


Energy Released and Bond

Strength

• As C-C bond strength

increases, the energy

released decreases:

– Combustion of ethane

(C-C = 348 kJ/mol)

more exothermic than

combustion of

acetylene (C-C =839

kJ/mol.

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Bearing the Torch

• Energy is not the onlyfactor.

• Acetylene (ethyne) isused in oxy-acetylenewelding torches ratherthan ethane orethene.

• Acetylene torchesreach 3,300 C andcan be used underwater.


Methane and the Bermuda

Triangle

• Methane is a product of

decomposing organic

matter (Natural gas).

• Under water it can build

up in large pockets which

are then released.

• The water density is

suddenly reduced and

any floating object (ships)

will sink.

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All Shapes and Sizes

• Hydrocarbons come in different sizes:

– number of C atoms.

• Different types:

– single, double or triple bonds.

• Systematic naming is required to

distinguish the thousands of possibilities.


It’s All Greek (Roots) To Me

• The first part of the name says how many C atoms are in the longestchain in the molecule.

• The second part of the name describes the bonds:– Ane single

– Ene double

– Yne triple

• Straight chain hydrocarbon begins with n-

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The Straight Chain Alkanes


Chains and Branches

• Hydrocarbons also come inbranched chains:

– Main chain (longest) in blue.

– Branches (shorter) in orange.

• Side chains get name from #of C atoms plus –yl

• Longest chain is namedaccording to table:

– In this example longest chainhas 9 C atoms – nonane.

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Methyl Meet ethyl – ethyl

methyl• Longest chain is nonane.

– Number the chain C atoms so that branches have lowest numbers.

• Branches are methyl and ethyl.

– Methyl at 3 and ethyl at 5.

• Order branches alphabetically:

5-ethyl-3-methylnonane

• NOTE: no spaces in name; hyphens used to separate numbers andletters.


Do Try These At Home

• Identify the longestchain in each case.

• In example 3, thelongest chain is bentnot straight. In 1 and2, numbering is samein either direction.

• 4-ethylheptane 5-propylnonane 3-methylhexane

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Multiple Bonds

• Alkenes: hydrocarbons containing double bonds.

• Position of double bond determined by numbering along main chain:

– Complete name is propene (3 C atoms, double bond must begin at C-1)

– Complete name is 3-octene (8 C atoms, double bond begins as C-3)

• Molecule contains triple bond and methyl group. Correct name is 4-methyl-1-pentyne.

– Multiple bonds must get lowest number possible (incorrect is 2-methyl-4-pentyne).


Rings and Things

• Ring is regarded as the main group and the chain is a

separate entity:

– Begin numbering at position of double bond.

– Choose direction to make the side chain the lower number.

– Add cyclo to indicate ring.

– 3-butylcyclohexene

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What’s In a Name

• Given the name 2,2,4-trimethylpentane, drawthe molecule’s structure.

• What we know:– There is only one possible

structure.

– The longest chain has 5 Catoms (pent).

– All the bonds are single (-ane).

– There are three methylbranches (Tri and methyl).

– They are joined at C-2, C-2and C-4.


Naming Multiple Groups

• When the same branch appears in the moleculemore than once, it is identified by a prefix.

• The naming scheme used for hydrocarbons isthe basis for naming all other organiccompounds.

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Structural Isomers

• For organic compounds,

the molecular formula is

not sufficient to specify a

unique molecule:

– C8H18 has several possible

isomers: same number of

atoms, but different

arrangement.

– Each isomer has a unique

name and structure but the

same molecular formula.


Geometric Isomers

• Single bonds allow free rotation about the bond axis.

• Double bonds are rigid and don’t allow rotation.

• Different isomers arise by virtue of geometry:– Chain continuation on opposite sides: trans-– Chain continuation on same side: cis-

• Physical properties are quite different.

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I Hear You Knocking

• For efficient

operation, combustion

must occur at the

right moment to drive

the piston up and

move the crankshaft.

• Premature

combustion is

inefficient and results

in “knocking.”


Checking the Ratings

• Molecular structureaffects combustion.

• Octane number describescombustion efficiency.

• Straight chain is worsethan branched:– 2,2,4-trimethylpentane has

octane rating 100.

– n-heptane has rating 0.

• Gasoline is a complexmixture of differenthydrocarbons andadditives with octaneratings from 85 – 97.

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A Hot Cocktail

• The Molotov Cocktail was a homemade

bomb consisting of liquid hydrocarbons

inside a bottle.

• Intermolecular forces determine whether a

substance is a gas, a liquid, or a solid.

• Hydrocarbons are nonpolar and have only

weak interactions between the molecules:

– making for low boiling point.


Boiling Point and Molar

Mass• Molecular interactions

increase withmolecule size:– Methane – n-butane

are gases (1 – 4 Catoms).

– n-pentane – n-heptadecane areliquids (5 – 17 Catoms).

– n-octadecane is solid( 17 C atoms).

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Hydrocarbons and Daily Life

• Hydrocarbons appear

in many familiar

products:

– Fuels – natural gas,

propone, butane.

– Lubricants and oils.

– Fabrics.


Fractional Distillation

• Crude oil is a fossil fuel –organic matter

decomposed over time.

• Complex mixture of

different sized

hydrocarbons.

• Refinement is achieved

by distillation.

• Lighter fractionscondense higher up the

fractionating column.

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The Ether

• Molecules beside hydrocarbons function asfuels.

• Ether contains two hydrocarbon groupsseparated by an O atom.

• General formula is: R-O-R'


Naming Ethers

• When the hydrocarbon groups are

different, the name orders the two group

alphabetically and ends in ether.

– Butyl methyl ether: H3CCH2CH2CH2-O-CH3

• When the groups are the same the prefix

di- is used.

– Dimethyl ether: H3C-O-CH3

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Ether and Alcohol: Isomers

• Diethyl ether was the first important

anesthetic.

• Diethyl ether and n-butanol are isomers –

molecular formula C4H10O.

• Physical and chemical properties are quite

different.

– Diethyl ether b.p. = 35ºC, insoluble in water

– n-butanol b.p. = 118ºC, soluble in water


Hydrogen Bonding and Boiling

Point• A hydrogen bond requires

an H atom attached to anelectronegative atom O,N or F.– Atom attached to H is the

hydrogen bond donor.– Atom accepting the H is the

hydrogen bond acceptor.

• The position of the Oatom controls properties.– In n-butanol the polar O-H

bond allows H-bonding.

– In diethyl ether the O atomis between two C atoms –no H-bonding.

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Anesthetics and Fuels

• Volatility of diethyl ether makes it a good

anesthetic – although flammability is

undesirable.

• Alcohols also undergo combustion.

• Ethanol is an important fuel additive to

reduce CO emissions.

3223222212810HCCHOCHCHOCOHO + +

3222222212810HCCHCHCHOHOCOHO+ +


Cleaning Up Our Act

• The Clean Air Act of 1991 introduced newstandards to reduce hazardous exhaustemissions – maximize conversion of CO toCO2.

• Oxygenates: Adding O to the fuel beforecombustion rather than afterwards.

• Two options:– Ethanol – expensive to produce

– Methyl tert-butyl ether (MTBE)

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Unwanted Consequences of

MTBE• Ethers are more polar

than hydrocarbons anddissolve slightly in water.

• Gasoline containingMTBE posesenvironmental hazard:– MTBE is carcinogenic.

– MTBE does not degrade.

• MTBE contamination ofwater supplies is a majorhealth issue.

• Ethanol poses a safer,but a more expensivealternative.


A Bigger Bang

• Fuel plus oxygen = bang.

• Nitroglycerin (1867)

revolutionized explosive

technology.

• Alfred Nobel received

more than 400 patents

related to explosives.

• The Nobel prizes are his

legacy.

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Nitroglycerin: The All-In-One

Explosive

• Nitroglycerin does not require additional

oxygen to detonate – they are supplied

from within.

– 4 molecules of liquid produce 29 molecules of

gas.

– Reaction is highly exothermic.

• Perfect combination for blasting power.

353922224()6()12()10()()CHNOlNgCOgHOgOgenergy+ + + +


Exo- or Endo-

• Heat change in reactionis determined by bondenergies.– Molecule with weak bonds

is more likely to react.

– Stronger bonds in productsthan reactants will producemore energy in reaction.

• Bonds in product arestronger than bonds innitroglycerin – reaction ishighly exothermic.

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Energy Bookkeeping

• Doing the sums on the bonds being broken:

• Doing the sums on the bonds being made:

• 7420 kJ are liberated in the reaction.


Summary of Exothermic and

Endothermic Reactions

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Nitrogen and Explosives

• Two factors make N an important component ofexplosives:– N-O bonds are weak.

– N≡N bonds are very strong.

• A new explosive molecule based on picric acid appearedin the 19th century.


TNT: User-Friendly Explosive

• Picric acid was too

unpredictable to be a

useful explosive.

• Enter TNT:

7536222()3()12()5()2()CHNOsNgCOgHgCsenergy+ + + +

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Primers for TNT

• TNT is much more

stable than picric acid

and requires a primer

like 1,3-

Dinitrobenzene.


High and Low Explosives

• Low explosives (like hydrocarbons):

– Must be confined in small volume.

– Require initial mixing with oxygen.

• High explosive:

– Produce energy immediately.

– Rate of reaction is rapid and goes to

completion.

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What Makes Reactions

Happen?• Endothermic reactions happen spontaneously.

• Some exothermic reactions don’t occur.

• Disorder (Entropy) determines if reactions happen:Second law of thermodynamics states that entropy of theuniverse is always increasing.

• Things tend to go from order to disorder.


Does Vacuuming the Carpet

Violate Physical Law?

• Vacuuming restores order to a room. Is this a

violation of the second law?

– Electrical power drives the vacuum cleaner.

– Steam drives the turbine that produces the electrical

power.

– Production of steam results in large entropy increase.

• Need to consider the entire universe: entropy

may decrease in the room, but has increased in

the universe elsewhere.

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How is A Person Like A Car

• Respiration obtains

energy from glucose.

• A combustion

reaction occurring in

the body.

6126222 ()6()6()6()CHOsOgCOgHOgenergy+ + +


Entropy and Explosions

• Combustion reactions and explosions are very

high entropy processes:

– Reactants are liquids or solids.

– Products are large numbers of gas molecules.

• Heat and entropy can be opposing influences:

– Endothermic reactions can proceed provided the

entropy increase is sufficient.

– Exothermic reactions can be prevented if there is an

entropy decrease.

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Complex Analysis

• Fuels are complex mixtures of different

hydrocarbons.

• Analysis of the vapor left after a fire is

sufficiently sensitive to identify the

composition of the mixture.


Gas Chromatography

• Chromatography

separates a mixture of

substances according to

their different attraction to

a stationary phase and a

moving phase:

– Molecules that prefer the

column move slowly.

– Molecules that prefer the

moving phase travel

quickly.

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Chromatograms

• If the column is long

enough the mixture

becomes separated

into pure

components.

• Substances can be

identified by

comparison with

known substances.


Fingerprint File

• Gasoline is a complex

mixture:

– Small molecules appear

first (prefer mobile phase).

– Large molecules appear

later (prefer stationary

phase).

• The chromatogram for

each sample will be

unique and is a fingerprint

that can be used to detect

it elsewhere.

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Gas Chromatography and

Airport Security

• Gas chromatography

can be used to detect

trace amounts of

volatile explosives.

• Samples can be

taken at airport

security and analyzed

for the presence or

absence of TNT.

the chemistry of everything kimberley waldron...ether and alcohol: isomers • diethyl ether was the...

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